Copper smelting slag is produced as a by-product in a flash or MI furnace in the course of smelting copper, and is generally landfilled or used as construction material after water granulation with high-pressure sea water or industrial water until it has a manageable size.
Elution of heavy metals such as As is a hassle in handling copper smelting slag. Typically, as the amount of copper smelting slag processed increases, heavy metals are gradually eluted from the slag and contaminate the granulation water that is recycled. Water granulation with such contaminated granulation water causes heavy metals in the granulation water to be trapped in the slag, and thus enhances elution of the heavy metal from the slag. Consequently, the heavy metal content in the circulating granulation water should be kept as low as possible for effectively suppressing elution of heavy metals from the slag.
Japanese Unexamined Patent Application Publication No. 2006-327909 provides a process that achieves satisfactory results on the elution test of slag by adding inorganic and organic coagulants to circulating granulation water to remove heavy metals such as As in a settling tank, and then recycling the coagulant-treated water as granulation water in a step of water-granulating copper smelting slag.
Japanese Unexamined Patent Application Publication No. 8-301636 provides a process of suppressing elution of heavy metals from slag discharged from a melting furnace by maintaining the granulation water alkaline with a pH of 11 or less, and filtering part of the granulation water to recycle.
Japanese Unexamined Patent Application Publication No. 2005-139027 provides a process of suppressing elution of heavy metals from slag produced from waste by removing suspended solids in a predetermined size which is contained in the granulation water through a coagulating or filtering means.